1. Field of the Invention
The present invention relates to a metal compound of new structure having aromatic hydroxycarboxylic acid as ligand, a charge control agent or charge enhancer containing said compound as an active ingredient, and a toner for developing electrostatic images for electrophotography etc. or powdery paint for electrostatic painting containing said charge control agent or charge enhancer.
2. Description of the Prior Art
In copying machines, printers and other instruments based on electrophotography, various dry or wet toners containing a coloring agent, a fixing resin and other substances are used to develop the electrostatic latent image formed on the photoreceptor having a light-sensitive layer containing an inorganic or organic photoconductive substance.
Toner chargeability is a key factor in electrostatic latent image-developing systems. Thus, to appropriately control or stabilize the amount of toner charge, a charge control agent providing a positive or negative charge is often added to the toner.
Of the conventional charge control agents in actual application, those providing a positive charge for a toner include basic dyes such as nigrosine dyes and triarylmethane dyes, and electron donors such as quaternary ammonium salts. Charge control agents providing a negative charge for a toner include 2:1 type metal complexes of azo dyes.
However, most charge control agents of dye structure are usually structurally complex and lack stability; for example, they are likely to be decomposed or deteriorated to lose their expected charge control capability when they are exposed to mechanical friction or impact, temperature or humidity changes, electric impact, light irradiation, etc. Also, dyes lack versatility for use in color toners, because they are essentially chromatic.
Charge control agents free of these problems include chelate compounds having (alkyl)salicylic acid, hydroxynaphthoic acid, salicylaldehyde, phthalic acid, or the like, as ligand [e.g., 2:1 type Cr, Zn or Al complex of (alkyl)salicylic acid, 2:1 type boron complex of salicylic acid, 2:1 type Cr complex of hydroxynaphthoic acid, 2:1 type Cr or Co complex of salicylaldehyde, 2:1 type Cr or Fe complex of phthalic acid].
Although the charge control agents of complex structure mentioned here are mostly light in color and advantageously usable in color toners, some are unsatisfactory in terms of heat stability, dispersion uniformity in resin or charge control property, remaining to be further investigated.
Also, to improve paint adhesion efficiency in electrostatic painting with powdery paints, there have been attempts of applying charge control agents which have traditionally been used to control the charge of toners for developing electrostatic images.
Such attempts include an electrostatic powdery paint containing a resin polymer of an azine dye [Japanese Patent Unexamined Publication No. 67563/1985], a resin powder composition for electrostatic painting containing a charge enhancer like a metal-containing complex salt compound (Japanese Patent Unexamined Publication No. 75077/1988) and a powdery paint composition containing a quaternary ammonium salt as a charge control agent or charge enhancer (Japanese Patent Unexamined Publication No. 212563/1990).
However, these electrostatic powdery paints remain to be further improved in terms of environmental stability and heat resistance and durability under high-temperature conditions during powder painting.
The object of the present invention is to provide a metal compound of new chemical structure having an excellent charge control or charge-enhancing property; a charge control agent or charge enhancer which contains said metal compound as an active ingredient, which is excellent in environmental resistance (stability of charge control or charge-enhancing property to changes in temperature and humidity), storage stability (stability over time of charge control or charge-enhancing property), and especially heat stability and durability (charge control or charge-enhancing property stability in frequently repeated use), and which do not affect toner fixability or offset property when used in toners; and a toner for developing electrostatic images and powdery paint for electrostatic painting incorporating said charge control agent or charge enhancer.